ATMEGA48V_06 ATMEL [ATMEL Corporation], ATMEGA48V_06 Datasheet - Page 33

• Manufacturer Part Number: ATMEGA48V_06
• Description: 8-bit Microcontroller with 8K Bytes In-System Programmable Flash
• Manufacturer: ATMEL [ATMEL Corporation]

7.5
7.6
2545J–AVR–12/06
Low Frequency Crystal Oscillator
Calibrated Internal RC Oscillator
The device can utilize a 32.768 kHz watch crystal as clock source by a dedicated Low Fre-
quency Crystal Oscillator. The crystal should be connected as shown in
Oscillator is selected, start-up times are determined by the SUT Fuses and CKSEL0 as shown in
Table
Table 7-7.
Note:
By default, the Internal RC OScillator provides an approximate 8.0 MHz clock. Though voltage
and temperature dependent, this clock can be very accurately calibrated by the user. The device
is shipped with the CKDIV8 Fuse programmed. See
more details.
This clock may be selected as the system clock by programming the CKSEL Fuses as shown in
Table
the pre-programmed calibration value into the OSCCAL Register and thereby automatically cal-
ibrates the RC Oscillator. The accuracy of this calibration is shown as Factory calibration in
Table 27-1 on page
By changing the OSCCAL register from SW, see
page
The accuracy of this calibration is shown as User calibration in
When this Oscillator is used as the chip clock, the Watchdog Oscillator will still be used for the
Watchdog Timer and for the Reset Time-out. For more information on the pre-programmed cali-
bration value, see the section
Table 7-8.
Notes:
Power Conditions
BOD enabled
Fast rising power
Slowly rising power
BOD enabled
Fast rising power
Slowly rising power
37, it is possible to get a higher calibration accuracy than by using the factory calibration.
7-7.
7-8. If selected, it will operate with no external components. During reset, hardware loads
1. These options should only be used if frequency stability at start-up is not important for the
1. The device is shipped with this option selected.
2. The frequency ranges are preliminary values.
application.
Frequency Range
Start-up Times for the Low Frequency Crystal Oscillator Clock Selection
Internal Calibrated RC Oscillator Operating Modes
7.3 - 8.1
306.
(2)
Start-up Time from
”Calibration Byte” on page
Power-down and
(MHz)
Reserved
Reserved
Power-save
32K CK
32K CK
32K CK
1K CK
1K CK
1K CK
”OSCCAL – Oscillator Calibration Register” on
Additional Delay
”System Clock Prescaler” on page 36
14CK + 4.1 ms
14CK + 65 ms
14CK + 4.1 ms
14CK + 65 ms
(V
from Reset
288.
CC
14CK
14CK
= 5.0V)
ATmega48/88/168
Table 27-1 on page
(1)
(1)(3)
CKSEL3..0
(1)
(1)
0010
Figure
CKSEL0
1
0
0
0
0
1
1
1
7-2. When this
306.
SUT1..0
00
01
10
11
00
01
10
11
for
33